Mechanisms of virus removal during transport in unsaturated porous media

Previous studies suggest that sorption of colloidal particles onto the air- water interface is an important mechanism for enhanced retention and retard ation during transport in unsaturated systems. In this study, bacteriophage s phi X174 and MS-2 and Br tracer were introduced into sand columns of vari ous water contents as a step function under constant flow rates. The result s showed that when a "reactive" (water washed) sand was used, the retention of both phi X174 and MS-2 increased significantly at low water saturation levels. However, when an "inert" (metals and metal oxides removed) sand was used, the effect of water content was minimal, although observable. These results suggest that in the presence of reactive solid surfaces, increased reactions at the solid-water interface rather than at the air-water interfa ce dominates in virus removal and transport under unsaturated conditions. A model that incorporated reactions at both the solid-water and air-water in terfaces was developed and successfully applied to the data.